1. Field of the Invention
The present invention relates to control systems in general and, more particularly, to a control system for a system having a flash tower and a stabilizer tower.
2. Summary of the Invention
A system controls a refining unit which includes a first tower receiving a feed liquid which provides an overhead vapor to a second tower and a first processed liquid to a third tower. The second tower provides a second processed liquid, a portion of which is heated to a desired temperature by a heater and recirculated back to the second tower. The control system includes sensors sensing the propane contents of the vapor feeding the second tower and of the second processed liquid. A temperature sensor provides a signal corresponding to a sensed temperature of the second processed liquid. A circuit provides a feed forward signal corresponding to a desired temperature for the second processed liquid in accordance with the feed propane content signal. A network connected to the second processed liquid propane sensor provides a feedback signal corresponding to the desired temperature for the second processed liquid. A switching network provides the feed forward signal as a control signal for a predetermined time interval at some predetermined time after a substantial change in the feed propane content has occurred and in accordance with the sensed feed propane signal. The switching network also provides the feedback signal as the control signal when it is not providing the feed forward signal as the control signal. Apparatus controls the heater in accordance with the sensed temperature signal and the control signal so as to control the temperature of the second processed liquid being fed back to the second tower.
The objects and advantages of the invention will appear more fully hereinafter from a consideration of a detailed description which follows, taken together with the accompanying drawings wherein one embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for illustrative purposes only and are not to be construed as defining the limits of the invention.